UNET Different size of spawned object on host and client

Hello If I spawn the object from host, on other Clients is bigger.

Only local player can spawn objects. Console shows the error when client tries to spawn block:

"NullReferenceException: Object reference not set to an instance of an object GameManager.Update () (at Assets/Script/GameManager.cs:87)"

 using UnityEngine;
 using System.Collections;
 using System;
 using UnityEngine.EventSystems;
 using UnityEngine.UI;
 using UnityEngine.Networking;
 
 
 public class Block
 {
 
     public Transform blockTransform;
 }
 
 public struct BlockAction
 {
     public bool delete;
     public Vector3 index;
 }
 
 public class GameManager : NetworkBehaviour
 {
     public static GameManager Instance { set; get; }
 
 
     private float blockSize = 0.25f;
 
 
     public Block[,,] blocks = new Block[100, 100,100];
     public GameObject blockPrefab;
 
     private GameObject foundationObject;
     private Vector3 blockOffset;
     private Vector3 foundationCenter = new Vector3(10f, 0, 10f);
 
     [SyncVar]
     private bool isDeleting;
 
     public Button deleteButton;
     public Sprite[] deleteButtons;
 
     [SyncVar]
     private int blockIndex = 0;
 
 
 
 
     private void Start()
     {
         Instance = this;
         foundationObject = GameObject.Find("Foundation");
         blockOffset = (Vector3.one * 0.5f) / 4;
     }
 
     private void Update()
     {
         if (Input.GetMouseButtonDown(0))
         {
             RaycastHit hit;
             if (Physics.Raycast(Camera.main.ScreenPointToRay(Input.mousePosition), out hit, 30.0f))
             {
                 
                 if (isDeleting)
                 {
                     if(hit.transform.name != "Foundation")
                     {
                         Vector3 oldCubeIndex = BlockPosition(hit.point - (hit.normal * (blockSize - 0.01f)));
                         NetworkServer.Destroy(blocks[(int)oldCubeIndex.x, (int)oldCubeIndex.y, (int)oldCubeIndex.z].blockTransform.gameObject);
                         blocks[(int)oldCubeIndex.x, (int)oldCubeIndex.y, (int)oldCubeIndex.z] = null;
                     }
                     return;
                 }
 
                 Vector3 index = BlockPosition(hit.point);
 
                 int x = (int)index.x
                     , y = (int)index.y
                     , z = (int)index.z;
 
                 if (blocks[x, y, z] == null)
                 {
                     CmdCreateBlock (index);
                     GameObject go = GameObject.Find ("Block" + (blockIndex - 1));
 
                     blocks[x, y, z] = new Block
                     {
                         blockTransform = go.transform,
                     };
                 }
                 else
                 {
 
                     CmdCreateBlock (index);
                     GameObject go = GameObject.Find ("Block" + (blockIndex - 1));
 
                     Vector3 newIndex = BlockPosition(hit.point + (hit.normal * blockSize));
                     blocks[(int)newIndex.x, (int)newIndex.y, (int)newIndex.z] = new Block
                     {
                         blockTransform = go.transform,
                     };
                     PositionBlock(go.transform, newIndex);
                 }
             }
         }
     }
 
     [Command]
     void CmdCreateBlock(Vector3 index)
     {
         GameObject go = Instantiate(blockPrefab) as GameObject;
         go.name = "Block" + blockIndex.ToString();
         go.transform.position = ((index * blockSize) + blockOffset) + (foundationObject.transform.position - foundationCenter);
         go.transform.localScale = Vector3.one * blockSize;
         blockIndex += 1;
         NetworkServer.Spawn (go);
     }
 
     private Vector3 BlockPosition(Vector3 hit)
     {
         int x = (int)(hit.x / blockSize);
         int y = (int)(hit.y / blockSize);
         int z = (int)(hit.z / blockSize);
 
         return new Vector3(x,y,z);
     }
     public void PositionBlock(Transform t, Vector3 index)
     {
         t.position = ((index * blockSize) + blockOffset) + (foundationObject.transform.position - foundationCenter);
     }
 
     public void ToggleDelete()
     {
         isDeleting = !isDeleting; 
         deleteButton.image.sprite = (!isDeleting) ? deleteButtons[0] : deleteButtons[1];
     }
 }